getting headers of http response

So if one opens a http address, is there first of all a way to only return a specific header, I suppose this can be done via either skip or custom refinements, but which ones, second of all if I do this: Locals: probe a/locals ; a being the name of my open port State: probe a/state I understand the purpose of the locals part of the port, that returns the headers. State I'm not sure as to why it is separated into state, anyone know the state part of a port object really well?